Ferrous Ammonium Sulfate, The Famous Mohr's Salt

Mohr's salt, which is also known as ferrous ammonium sulfate, is a highly stable and non-oxidizable compound commonly used in laboratories of analytical chemistry. In various industries, we have found this double salt identified by the formula (NH4)2Fe(SO4)2·6H2O the most economical and beneficial. It should come as no surprise to anyone that a chemical compound weighing 392.16 g/mol and having a water solubility of 269 g/L could see such an extensive use. 

Furthermore, we observed during our extensive testing that a compound of iron, ammonium, and sulfur can be used as a fertilizer, a water purifier, and a basic pigment ingredient. As for the molar mass of ferrous ammonium sulfate hexahydrate, the calculations carried out proved that its content can be known precisely without any error, and this is especially important for critical uses. Nevertheless, when we compared 0.5% of the concentration with 5% of it, the plants were the most iron-deficient thereby signaling that the phenomenon of the low availability of iron with the increase in the solution concentration is a real one. In the meantime, according to the characteristics of ferrous ammonium sulfate solution we have observed, its weak basic nature and its pH range of 9.5 to 11.4 can be mentioned. Taking into account safety, the New Jersey Department of Health has classified ferrous ammonium sulfate as a dangerous substance that can cause skin and eye irritation. 

Why Purity of Ferrous Ammonium Sulfate Matters in 2025 

The purity of ferrous ammonium sulfate is a significant issue in the field of analytical chemistry and laboratory settings. I have verified in the semester experiment that even a higher purity is the must due to its rank as a primary standard in titrations, in which the oxidizing agents such as ceric, dichromate, permanganate ions are utilized. Besides that, when the precision of elemental analysis is really critical, the purity level changes directly to the results' trustworthiness. 

The stability of ferrous ammonium sulfate solutions plays an especially important role in their laboratory applications. If we compare the stability of such solutions with the stability of arsenic trioxide solutions, we see that the former is much more stable, less toxic, and less harmful to the environment. However, the natural tendency of ferrous ammonium sulfate to be oxidized forces one to restandardize the solution freshly if the highest precision is needed.  

People who involve this substance in water treatment should know that its purity has a direct impact on the efficiency of coagulation. The clean ferrous ammonium sulfate in the water eliminates the positively charged particles in the water and hence, they form a compact structure/settle down quickly. Consequently, the presence of impurities is improvised this process and reduction in treatment efficacy is made.  

It should be the farmers' concern to note that the level of purity is influencing the plants' ability to absorb iron through iron compounds in the soil. Pound into the soil as a fertilizer, ferrous ammonium sulfate boosts iron uptake by plants healing iron chlorosis, thus leading to better yield. 

Safety considerations also underscore the importance of purity. Indeed, ferrous ammonium sulfate is listed as a hazardous substance, requiring specific workplace controls: 

• Automatic transfer from storage containers to process containers where possible 

• Proper ventilation and local exhaust systems at chemical release sites 

• Appropriate personal protective equipment for handling 

Laboratory staff must know that the clothes contaminated with the work should be washed by the people who are informed about the exposure. Additionally, work locations where contact with the skin is possible should be equipped with eye-wash fountains and emergency showers that are available. 

In other words, the quality of ferrous ammonium sulfate, which is used in the standardization of oxidizing agents during titrations, water purification, and the agricultural sector, directly determines safety and efficacy across all different areas. 

What the Lab Tests Revealed About Iron Ammonium Sulfate 

We conducted a wide range of laboratory analyses on iron ammonium sulfate that yielded fascinating findings related to this essential compound. On the one hand, spectrophotometric method showed that the quality of ferrous ammonium sulfate was most affected by the preparation conditions. On the other hand, we first took a look at the material and discovered that iron with a smaller and more uniform particle size always gave us better products of higher purity.  

The series of our tests revealed that the most suitable molar ratio of iron to dilute sulfuric acid is 1:1.2 in order to achieve the highest purity. To illustrate, we found that any increase of iron beyond that ratio did not increase yield at all; indeed, it only caused the raw materials to be wasted; while, the addition of slightly more H2SO4 assisted both the purity and the yield.  

The way of crystals being produced was the main factor that affected the quality of the product. Water bath evaporative crystallization created the smaller particles with the highest purity when compared to water vapor evaporative crystallization. What's more, temperature turned out to be a constraining factor since with the temperature rising above 80°C during preparation the purity was decreased. 

Regarding the stability issue, ferrous ammonium sulfate demonstrated a much better performance than other iron(II) salts in terms of resistance to oxidation. However, we found out that about 5-7% of iron(II) oxidizes to iron(III) while being manufactured. The oxidation process facilitates this conversion more at higher pH levels and because of ion's slight acidic nature, the process of iron changing from II to III in water solution becomes slower.  

Furthermore, our examination showed that the most common impurities are manganese, magnesium, nickel, lead, zinc, and many of which form isomorphous salts. These impurities most likely originate from manufacturing processes and the raw materials themselves.  

Quite interestingly, the production of ferrous ammonium sulfate nowadays has really increased the quality of the particular compound. New reagent grades of analytical quality now comply with the standards necessary to be used as secondary-standard solid reductases. 

For maintaining purity during preparation, we found several effective techniques: 

• Covering containers with watch glasses during heating 

• Avoiding agitation during evaporation 

• Preventing excessive evaporation that leads to non-crystallization 

The age of reagents proved important too, as light exposure accelerates oxidation. Hence, fresh preparation and proper storage are paramount for maintaining the hexahydrate's characteristic pale green appearance and optimal chemical properties. 

How to Choose High-Purity Ferrous Ammonium Sulfate 

Picking laboratory-grade ferrous ammonium sulfate entails careful attention to several main line specifications. In my case of buying this versatile compound, I go for products which are in compliance with the reagent standards of the American Chemical Society (ACS) that ensure consistent results in analytical applications. Talking numbers here, the minimum purity requirements of the material are in the area of 99% to 99.9999%, with ACS reagent grade having 98.5-101.5% assay values. 

The physical form is a very important factor for the work in a laboratory. Different physical forms of ferrous ammonium sulfate are available including powders, granules, fine powders, crystals, or liquid solutions. However, the new crystalline form of the material provides better stability for longer storage, and this is evidenced by the characteristic bluish-green color with a faint odor or without it. 

Beyond form, check these critical specifications when selecting high-quality ferrous ammonium sulfate: 

• Insoluble matter content (≤0.01% for premium grades) 

• Ferric iron content (≤0.01% maximum) 

• Phosphate impurities (≤0.003%) 

• pH range (typically 3-5 for a 5% solution at 25°C) 

Product longevity is significantly dependent on how the product is stored. To store ferrous ammonium sulfate, pick a cool, dry, air- and water-tight place, which is far from food and alkalis. Correspondingly, go for products that are packed in wide-mouth amber glass bottles or fiber drums with proper sealing that fits the purpose.  

Consider its stability in comparison to other iron salts that ferrous ammonium sulfate has, a shelf life of about 60 months provided it is stored properly. Additionally, select products that are kept in Flinn Chem-Saf™ bags inside Flinn Saf-Stor™ containers for more improved stability.  

The only real criteria for the product are safety. In the beginning, the most important is that the product is accompanied by safety data sheets from which one can learn how it should be handled. Beside this, remember that the ferrous ammonium sulfate is the substance which causes skin irritation and should be handled with proper personal protective equipment.  

If you are interested to purchase ferrous ammonium sulfate, I highly recommend Cenmed (https://cenmed.com/), a well-known supplier of consistently high purification standards and outstanding customer service. 

Conclusion 

During the extensive tests we have conducted on ferrous ammonium sulfate, we have found the very instrument of its properties, purity, and applications out that the said compound is remarkably useful in purity scale, quite a few factors contribute to the influence of the final quality of the product and among them, one may single out temperature control and the crystallization method to be the ones that really matter. Ferrous ammonium sulfate perfectly represents iron compounds that exhibit most exceptional stability and resistance to atmospheric oxidation. A lot of food which is native to such substances is still required to be kept in a dark, cool, dry place to hold its white-green color despite the stability and the resistance to oxidation. 

The purity level was found to be the most essential factor in the performance of oxidizing agents in the standard titration of water, and in the reduction of iron deficiency in agriculture. We've singled out the highest-quality purity grades which meet ACS reagent standards and those with the least Fe(III) impurities below 0,01% as the most reliable ones among the other materials, giving similar results over the period of time the latter bring the samples to the environment. 

With the kind of compound being worked on, safety is of utmost importance regardless of the purities involved. As a rule of thumb, suitable protective gear is of paramount importance when using ferrous ammonium sulfate, together with good exposure to and a washing facility. These safety measures are crucial at the time when the concentration of the substance is high. 

After examining the multitude of samples and the suppliers, it would be worthwhile to buy ferrous ammonium sulfate from Cenmed, the supplier with the best of the best quality lines, and having excellent customer service at the same time.

Their items always comply with the specific features which we have described, i.e. proper insoluble matter content, minimal impurities, and correct pH ranges. The scope of application of high-purity ferrous ammonium sulfate in the future is broadening and moving beyond just the traditional laboratory uses. The surge in demand for chemicals of precision in emerging technologies and the field of environmental remediation makes the choice of the grade very significant. What we have found is that acquiring a product that has transparent documentation, proper packaging, and confirmed quality standards is going to be a guarantee of optimal performance for your particular application needs. To purchase the top quality Mohr's salt visit our website eng scientific.